Conventional laminates for printed circuit boards achieve flame retardancy by using brominated flame retardants, especially tetrabromobisphenol A type epoxy resin which has better flame retardancy, but will produce hydrogen bromide gas during combustion. In recent years, carcinogens such as dioxin, dibenzofuran and the like have been detected in combustion products of electrical and electronic equipment waste containing halogens such as bromine, chlorine and the like. Thus, the use of brominated epoxy resins is limited. Waste Electrical and Electronic Equipment Directive and the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment were formally implemented by European Union on Jul. 1, 2006. The development of halogen-free flame retardant copper-clad laminates has become a hot spot in the industry, and laminate manufacturers have launched their own halogen-free flame retardant copper-clad laminates.
With the refinement, thinning and increased functional requirements of consumer electronics, the thickness and line width of the dielectric layer of the laminate substrate are getting smaller and smaller, and the used fiberglass cloth is getting thinner and thinner. The dielectric layer has to have a sufficiently low dielectric constant (Dk) if it is necessary to keep the impedance constant under the conditions that the line width gets smaller. The thinning of the reinforcing material will lead to the lack of rigidity of the substrate. In the process of PCB processing, it is easy to warp, expand and contract and the like, so as to affect the yield of PCB processing. Therefore, the dimensional stability of the substrate is very important. At the same time, when PCB supports more components, the requirements on the binding force of bonding pad get more prominent, which requires the substrate have a high adhesive force simultaneously. At present, a large part of halogen-free Tg substrates for consumer electronics still use amine curing agents such as DICY and DDS, which have excellent adhesive force, but are inferior in rigidity, dielectric properties and heat resistance, so that they cannot meet the requirements on ultra-thin HDI process.